READ: Types of Drugs

Techniques Used in Toxicology

As you have learned, there are many different types of drugs. The main challenge facing Forensic Toxicologists is to identify an unknown substance that could be one of a thousand or more commonly encountered drugs or substances. Toxicology testing is generally performed using blood, urine, hair or vitreous humor samples. Whereas drugs and toxins can be rapidly metabolized and absent in blood and urine samples, toxins tend to linger in both hair and vitreous humor samples for longer periods. When discussing Toxicology techniques, it is important to distinguish that there are two levels of toxicology testing used in standard toxicology investigations: Screening tests and Confirmatory tests.

Screening Tests

Screening tests are done to eliminate some drugs from consideration and narrow down the possibilities. Screening tests include a variety of spot tests, Thin Layer Chromatography, Gas Chromatography (without Mass Spectrometry), and Immunoassay. Immunoassay is a common testing procedure where the concentration of a substance in a liquid is measured using the reaction of an antibody to the antigen (the drug). It can be performed on its own without need for further confirmation for less critical needs such as to test for the presence of Strep throat in a doctor's office. In forensic investigations, however, it is used as a first step screening test and should be followed up using a confirmatory testing method in order for it to be admissible to court.

Spot Tests

Spot tests are sometimes performed by law enforcement officers in the field, but this can be dangerous due to the volatile chemicals used in drug production and is only advised in certain situations. In a forensic lab, spot tests are often done on a spot plate or in a test tube. Spot tests do not confirm on their own the presence of a particular drug but they are a good indicator for the absence of a drug and a starting point for further investigation in a certain direction. It is important to note that spot tests typically destroy the sample so if only a small quantity of evidence is available they may not be indicated.

There are 5 Primary color spot tests:

1. Marquis - Turns purple in presence of an Opium derivative and orange-brown in presence of Amphetamines/Methamphetamines.

2. Dillie-Koppanyi - Turns violet-blue in the presence of most Barbiturates.

3. Duquenois-Levine - A purple color appears if Marijuana is present.

4. Van Urk - Turns purple in the presence of LSD.

5. Scott Test - A blue color appears if Cocaine is present.

See sample images of some color spot tests below:

Confirmation Tests

Confirmation tests identify a specific substance and include spectroscopic tests. The most accurate and commonly used confirmatory test is Gas Chromatography with Mass Spectrometry. Depending on the type of substance and quantity available, forensic scientists need to select a method that will provide insight without completely eliminating the evidence.

Drugs can also be examined microscopically. There are two types of microscopic observations that can be conducted; Morphology and Microcrystalline. Morphology examinations involve observing the structure of substances such as botanical features to potentially identify certain substances such as Marijuana. Microcrystalline examinations involve the observation of crystalline structures which can be highly characteristic of certain drugs such as Cocaine.

Collection & Preservation of Drug Evidence

Drug evidence is relatively simple to collect for analysis. Urine and blood samples are typically collected in clean containers designated for these specific purposes. If the evidence involves plant materials, investigators will photograph the plant evidence and allow it to dry before packaging to avoid mold growth. Items of drug paraphernalia are packaged according to their type of material. Drug samples are generally placed in a clean, airtight containers to avoid contamination and loss of evidence. Investigators should be especially aware of the risks associated with handling used needles and clandestine drug lab evidence when involved in those cases and heed all safety guidelines. Clandestine drug labs are typically thought of as "Meth Labs" or "Crack houses" and typically contain many volatile substances that present numerous hazardous conditions. Evidence collection at these places takes place after the site has been deemed safe for personnel to enter by hazardous materials experts. Each item of evidence is collected and packaged as indicated by the type of material it is.

Georgia Virtual, Forensic Toxicology, CC BY-NC-SA 3.0